Automated placement machines, such as robots, and the like, are commonly used in transfer operations on automated factory lines. These machines typically include a mechanism, such as a gripper assembly, for gripping or grasping objects which must be transferred from one location to another. A gripper assembly typically employs movable mechanical fingers, suction devices, or combinations of these and other technologies. Vacuum driven suction devices are in common use for applications requiting flexibility in handling parts of varying sizes and weights.
Many vacuum driven gripper designs use vacuum nozzles of varying sizes or diameters which are selectively used based on the size and weight of the object involved. Ordinarily, the larger the diameter of the nozzle, the greater the gripping force for that nozzle, given a constant vacuum pressure. In one common gripper design, the gripper assembly includes multiple nozzles of varying shapes and sizes arranged on a rotary head. The head is rotated as desired to select the most appropriate nozzle for a given task. FIG. 1 illustrates various orientations of a prior art four nozzle rotary head gripper assembly 10 operating within a predetermined work space 12. There are several problems associated with these multiple nozzle gripper assemblies. First, these assemblies tend to be large, thus consuming valuable work space. As depicted in FIG. 1, the effective work space 25 is reduced to accommodate the varying distances of the nozzles from the center of the rotary head Second, separate control logic and support hardware (not shown) are usually required for each nozzle 20. Third, the weight associated with the support hardware reduces the effective pay lead of the machine. Ordinarily, the machine must be slowed to accommodate the weight. thereby reducing the effective speed of the machine, and hence increasing the manufacturing cycle time. Fourth, maintenance cost is high. Each nozzle 20 must be calibrated with respect to the center of the rotary head 15.
A second approach to vacuum driven gripper design uses a single nozzle with tip or tool changing capabilities. The diameter of the gripping surface of the nozzle is changed by selecting from among tips of different sizes. It can be readily appreciated that valuable time is consumed while tool changes are occurring. Additionally, there is a high calibration cost involved with teaching the location of the various tips. Thus, this approach is expensive in manufacturing cycle time, and direct labor costs.
Vacuum driven gripper assemblies are useful for a variety of automated transfer functions in manufacturing operations. However, prior art grippers tend to have a high acquisition and operating cost. Additionally, valuable manufacturing cycle time can be consumed between nozzle changes in multiple nozzle gripper assemblies.